Wind-powered electricity generators are known in the art. Prior art systems are interconnected to utility grids and are used to displace more expensive fossil fuel generation when the wind reaches a minimum speed. This minimum speed may be relatively high since utility grids are generally high power systems not capable of efficiently utilizing low-level supplemental power sources. So, much of the electricity capable of being generated by utility grid-interconnected systems disadvantageously goes unused.
Prior art, off-grid, wind electrical power systems, such as may be used in remote towns or villages, are typically used in combination with a fossil fuel baseload generator such as diesel engine, which essentially replaces the utility grid, and is supplemented by wind-generated electricity on an as available basis. Towns and villages which are off-grid are typically in remote locations with extremes of weather so that necessary reliance on shipments of fossil fuel is disadvantageous.
Many electricity users, especially in remote locations, would prefer to generate their electricity entirely with renewable resources such as the wind instead of with fossil or nuclear fuels, the recovery, spillage and effluent of which may adversely impact the environment. The intrinsic variability of wind energy, however, makes reliance solely on the wind for electricity problematic. Several prior art wind power systems have sought to alleviate this problem by storing wind energy for use in generating electricity during periods when the wind does not blow hard enough to meet demand for electricity.
U.S. Pat. Nos. 4,229,661, 4,447,738 and 4,455,834 disclose systems for storing wind energy as compressed air. The windmills operate compressors. An air motor or turbine is used in the '661 and '738 patents to generate electricity from the compressed air during periods of low wind speed. In the '834 patent, air is compressed to the extent it may be stored as a liquid in a cryogenic tank.
U.S. Pat. Nos. 4,204,126 and 4,206,608 disclose systems for storing wind energy with hydraulic fluid in pressure tanks ('608 patent) and columns ('126 patent). A disadvantage of pressure tank and column storage systems is the relative expense and difficulty of installing and maintaining a pressurized system. Electricity generating systems are preferably highly reliable and maintenance free.
U.S. Pat. No. 4,236,083 discloses a windmill having an air brake driven through a speed increaser. Air is heated by agitating it in a closed path around the brake. The heat is used or stored in rock. A disadvantage of this device is that energy storage is achieved by deliberate friction between, and wear of, device components, requiring a high level maintenance and reducing reliability.
U.S. Pat. Nos. 5,133,191 and 4,479,352 disclose hot liquid storage systems for cogenerating electricity from waste heat with steam turbines. The waste heat is collected from stack gas or industrial exhaust. Cogeneration systems are not practical for use to provide electricity to remote towns and villages since there are not likely to be industrial plants in these areas. A further disadvantage to use of these systems is that the effluent used to heat the liquid was created by burning fossil or nuclear fuel.
What is desired therefore is a wind-powered electricity generating system which is capable of storing wind energy for use during periods of low wind speed and/or high demand, and which is simple in construction, low in maintenance, and reliable in use. An electricity generating system designed for operation without dependence on fossil or nuclear fuel is also desired.